The present disclosure generally relates to oil free compressors, and more particularly relates to an air compressor having an air-cooled wobble piston with a flexible compressing ring.
Conventional oil free compressors use a wobble piston that is rigidly secured to a connecting rod for allowing the piston to wobble or rock in a cylinder with the connecting rod as the piston is reciprocated within the cylinder. At least one piston compression seal or ring is provided around a periphery of the piston for allowing the piston to tilt in the cylinder without losing an air-tight seal, and the sealing relationship is enhanced by providing a smooth coating on an inner surface of the cylinder. The air-tight seal, the smooth coating in the cylinder, and the material composition of the flexible compression ring reduce friction such that oil lubrication is not required. Several types of the wobble pistons are described in commonly assigned U.S. Pat. Nos. 5,231,917 and 6,213,000; both of which are incorporated by reference in their entirety.
In use, a compression chamber of the cylinder is repeatedly compressed on upward strokes of a piston head, and as a result, heat is generated when air or gas is compressed in the chamber. Effective cooling of the cylinder and the piston is important to enhance the service life of the compressor because the service life of many compressor components is degraded by heat. Although heat absorbed by the piston during the compression stroke is transferred from the piston top to air drawn into the cylinder during operation, conventional wobble pistons prevent sufficient cooling of the piston and the piston seal, thereby causing premature failure of the compressor.
Often, the air-cooled oil free compressors use the rocking or wobble piston having a flexible cup-shaped seal as a compression ring disposed around the periphery of the piston. An oil free compressor crankcase typically has an open frame connecting important components together for the air circulation. One or more cooling vents are provided for delivering air into the open frame for cooling the components, such as the piston, the compression ring, the cylinder, a valve plate, and motor windings. However, conventional cooling vents prevent efficient delivery of the cooling air into the open frame.
Another operational challenge of the conventional wobble piston is that, due to its geometry, the conventional compression ring is subject to fatigue stress, and causes loud noises and subsequent ring failure after extended use. A conventional piston cap has a radial outer surface or wall that is linear and substantially parallel to an operational axis of the wobble piston. The compression ring is formed around the piston cap into the cup-shaped seal or ring that is opened outwardly radially, and extended toward a valve plate, thereby allowing the in-cylinder pressure to force the ring outwardly radially toward the inner surface of the cylinder. During reciprocal movement of the piston, the compression ring is elastically deformed into the shape of an ellipse for maintaining a sealing contact with the inner surface of the cylinder. This repeated deformation of the compression ring causes premature structural failures, such as fractures and gaps in the ring.
Thus, there is a need for developing an improved wobble piston having enhanced cooling vents with larger openings, and a compression ring that provides reduced fatigue stress and noise, thereby extending the service life of the compressor.